Factors Affecting Performance Flashcards
Factors Affecting Performance
- Diet
- CNS Function
- Strength/Skills
- Environment
- Energy Production - anaerobic sources
Diet
- Carbohydrate
2. Water Intake
Energy Production - anaerobic sources
- [PC]
- Glycolysis
Anaerobic Sources
- VO2 max
- Cardiac Output
- O2 delivery
- [Hb]
- PO2
- O2 extraction
- Mitochondria
Environment
- Altitude
- Heat
- Humidity
Strength’Skill
- Practice
- Natural Endowment
- Body type
- Muscle Fiber Type
CNS Function
- Arousal
2. Motivation
Sites of Fatigue
Central and peripheral
Fatigue
Inability to maintain power output or force during repeated muscle contraction
Central Fatigue
CNS
Peripheral Fatigue
- Neural Factors
- Mechanical Factors
- Energetic Contraction
Peripheral Fatigue is
the big picture but central fatigue will cost you the race
Possible sites of fatigue
- Psyche brain (motor unit recruitment/motivation)
- Spinal Cord (reflex drive)
- Peripheral Nerve (Neruomuscular transmission)
- Muscle sarcolemma (Muscle action potential)
- Transverse tubular system (K, Na, excitation)
- Calcium release (activation, energy supply)
- Actin-myosin interaction
- Cross bridge tension and heat
- Force Power output
Central Fatigue listed as a site of fatigue due to
- Reduction in motor units activated
- Reduction in motor unit firing frequency
- CNS arousal can alter the state of fatigue
CNS arousal can alter the state of fatigue
By facilitating motor unit recruitment to increase strength
- increasing motivation (shouting during the exertion)
- Physical or mental diversion (i.e. contracting non-fatiguing muscles during the rest period or doing arithmetic b/w fatiguing bouts.)
Excessive endurance training - overtraining
- Reduced performance, prolonged fatigue, sleep disturbances, loss of appetite,
- Evidence that increases r decreases in brain serotonin during prolonged exercise either hastens or delays fatigue respectively
- New evidence points to ration of serotonin linked to fatigue, sleepiness, depressed mood) to dopamine that either leads to fatigue or arousal
- Brain levels of NE also contribute to fatigue or arousal
Central governor model has some criticism
- Focuses on conscious and subconscious brain not spinal cord or motor unit
- Proposes that the brain regulates exercises intensity in an effort to protect the body from exercise-related damage or by disrupting cellular homeostasis
- The central governor limits/control exercise intensity vy neurally recruiting a certain amount of motor units innervating skeletal muscle
Peripheral Fatigue: Neural Factors
- Majority of evidence for fatigue points to peripheral factors where neural mechanical or energetic events can reduce tension development
Neural Factors
Sarcolemma and transverse tubules - relates to ability of muscle membrane to conduct an action potential
- Inability of Na/K pump to maintain action potential amplitude
- Na/K pump capacity can be improved by training
- Gradual depolarization of sarcolemma can result in action potential block in the T-tubules which signals calcium release from SR
- Reduction in calcium release from SR affects muscle contraction
Neuromuscular Junction
Not a site of fatigue
Peripheral Fatigue Mechanical Factors
- Cross Bridge Cycling and tension development
- High H+ Concentration may contribute to fatigue
- Longer relaxation time is a sign of fatigue
Cross bridge cyclin and tension development depend on
- Arrangement of actin and myosin
- Calcium being available to bind with troponin
- ATP availability needed for activation (causes movement) and dissociation (causes relaxation) of cross bridges
High H+ concentrations may contribute to fatigue by
- Reducing the force per cross-bridge
- Reducing the force generated at given Calcium concentration
- Inhibiting calcium release from SR
Longer Relaxation time is a sign of fatigue
- Relates to time of peak tension development to baseline tension
- Due to slower cross-bridge cycling
Peripheral Fatigue: Energetics of Contraction
- Imbalance between ATP requirements and ATP generating capacity
- Rate of ATP utilization is slowed faster than rate of ATP generation due to cellular fatigue mechanism
Imbalance between ATP requirements and ATP generating capacity
Accumulation of inorganic phosphate occurs when ATP generating mechanisms cannot keep up with ATP usage which
- inhibits maximal force
- Reduces cross-bridge binding to actin
- inhibits Ca release from SR
Rate of ATP utilization is slowed faster than rate of ATP generation due to cellular fatigue mechanism
This is done as a protective mechanism in order to maintain ATP concentration and homeostasis. In other words, ATP availability to the cell never really run out. Factors that cause fatigue cause a reduction in rate of ATP utilization
Radical Production During Exercise Contributes to Muscle Fatigue
- Key contributor to muscle fatigue during high intensity or prolonged exercise greater than or equal to 30 minutes
Exercise promotes free radical formation
Molecules that contain unpaired electrons in outer orbital and are capable of damaging proteins lipids and DNA
Free Radicals Can Contribute to Fatigue by
- Damage to contractile proteins (myosin and troponin) reduces calcium sensitivity of these myofilaments which limits the number of cross bridges in the strong binding state and depress Na/K pump activity in muscle due largely to disruption of K homeostasis
Optimal levels of antioxidants can postpone fatigue
high doses of antioxidants can impair muscle function
Muscle fiber recruitment in increasing intensities of exercises
Type 1 —) Type 2a —) Type 2x
Up to 40% VO2 max type 1 fibers are recruited
reductions in O2 supply to this fiber would reduce tension development
Type 2a fibers recruited at 40-75% VO2 max
If O2 delivery reduced or ability of fiber to use O2 reduced (reduced mitochondria) then tension development reduced
Exercise > 75% VO2 max requires 2x fibers
Results in increased lactate and H+ production
Events lasting less than 10 seconds
Shot put
High Jump
Long Jump
50-100 meter sprint
Ultra short term performances are
dependent on recruitment of type 2 muscle fibers that generate great forces in a short period of time
Max performances of ultra short term performances are limited by
- Fiber type distribution and number of fibers recruited which is influenced by motivation and arousal
- Optimal performance affected by skill and technique which are dependent on practice
Ultra Short-Term Performances
Primary Energy Source is anaerobic - ATP-PC system and glycolysis - thus creatine supplementation may improve performance
Factors affecting fatigue in ultra short term performance
- Practice
- Skill and technique
- Muscular Power
- Fiber type distribution and recruitment
- PC and glycolysis
- Motivation and arousal
Short Term Performance
Events lasting 10-180 seconds
- 200-400 meter sprint
- 50-100 meter swim
Shift from anaerobic to aerobic metabolism in short term performances
- 70% energy supplied anaerobically at 10s
2. 60% supplied aerobically at 180s
Anaerobic glycolysis is
Primary energy source that results in elevated lactate and H+ levels and interferes with Ca binding with troponin for short term performances
Ingestion of buffers may
Improve performance in short term performances
Factors affecting Fatigue in the Short term
- Fiber type distribution and recruitment
- increasing muscle and blood H+ - buffer
- VO2
- Glycolysis and PC
Moderate Length Performances
Events lasting 3-20 minutes (5 K run)
- 60% ATP generated aerobically at 3 min
- 90% ATP supplied aerobically at 20 min
Performance limites in moderate length performances
the CVS and mitochondrial content
High VO2 max is
Important in moderate length performances
- High maximal SV key to high CO
- High arterial O2 content is influenced by HGB content and inspired O2
Moderate Length Performances
Require energy expenditure near VO2 max - type 2x fibers recruited - high level of lactate and H+ accumulation
Is maximal oxygen uptake important in distance running performance
VO2 max sets the upper limit for ATP production in endurance events - even though race is not run at 100% VO2 max
Performance is also determined by %VO2 max at which runner can perform - estimated by lactate threshold or GET and running economy (moving at a faster rate of speed for the same amount of O2 consumption compared to someone who is slower at the identical O2 consumption
Intermediate Length Performances
- Events lasting 21-60 minutes
- Predominantly aerobic - usually conducted at ,90% VO2 max
- High VO2 max is important
- High lactate threshold or GET
Intermediate Length Performances
Other Important Factors
1. Running economy - due to both biochemical and bioenergetic factors and High percentage of type 1 muscle fibers
- Environmental Factors - due to heat, humidity (related to portion of cardiac output that will be directed to skin for cooling, this will affect HR at any given workload) and state of hydration this will affect HR at any given workload due to changes in plasma volume.
Factors affecting Fatigue in aerobic performances lasting 21-60 minutes
- heat load
- steady state VO2
- Dehydration
- Lactate threshold
- % type 1 fibers
- biomechanics
- running economy
- bioenergetics
- running economy
Long term performances
Events lasting 1-4 hours
Environmental factors are
more important the longer the performance
Maintaining a rate of carbohydrate utilization is an issue at durations greater than
1 hour because muscle and liver glycogen stores decline
- maintain carbohydrate oxidation by the muscle at >60% VO2 max
1a. Fats can provide fuel below 60% VO2 max typically but carb oxidation allows for higher intensities to be maintained or performance will suffer - Protection of membrane excitability (increased glucose supplementation during prolonged exercise suggests improvements in Na/K pump to maintain action potential amplitude and frequency during repeated stimulation
Factors affecting fatigue in aerobic performances lasting 1-4 hours
- heat load
- dehydration
- Liver and muscle glycogen stores - supplement during exercise
- Diet
- Lactate threshold
- VO2 max
- % Type 1 fibers
- Biomechanics
- Bioenergetics
- Running economy
Diet, glucose supplementation and fluid ingestion during duration events are very important in order to prevent glycogen depletion
Factors affecting performance in ultra endurance events
Examples:
166 km mountain run
Triple Iron Triathlon
24 hour rin
Most important variables in ultra endurance events
- VO2 mac
2. % VO2 max that can be sustained
Metabolic Responses during ultra endurance events
- Plasma FFA and fat oxidation is 3.5x higher after event consistent with exercise at
Potential for hyponatremia during ultra endurance events is
high because sodium stores are diluted because of too much water ingestion only happens to 4% of athletes.